The present invention relates to an apparatus for detecting a motion of a television image which is applied to detect a movement vector indicative of an amount of movement and a moving direction of a television camera when the overall pick-up picture moves due to panning or the like of a television camera.
As one of the methods of narrowing the transmission band of a high quality television signal, there is a method whereby a movement vector indicative of the movement of a television camera is transmitted together with the image data whose data amount was reduced to 1/4 so as to shift the subsampling location at a four-field period, and on the reception side, a picture plane of one field is reproduced using the data during the period of four fields with respect to a still image, and in the case where the whole picture moves in the same direction as in the case where the television camera pans, the coordinate axis is shifted in accordance with the movement vector and thereby reading out the data in the previous frame from a memory, and thereby performing the movement correction.
For the movement vector which is used for such a movement correction, it is enough that one movment vector is provided for one field. Hitherto, to improve an estimation accuracy a picture plane is divided into four regions and a plurality of movement vectors obtained in each region are subjected to a process of a majority decision or a simple arithmetic averaging process, thereby deriving the movement vectors regarding the whole picture plane.
To obtain the movement vector in each region which is derived by dividing one picture plane into a plurality of regions, a block matching method is used. Further, a simplification by way of representation points is made and the picture plane is divided into a plurality of blocks, then a frame difference for detection of movement vectors is derived on each block unit basis, thereby examining a degree of correlation from the absolute value of this frame difference. The frame difference is the difference between the pixel (representative point) at the spatial center of a target block of the previous frame, for instance, and each pixel included in a target block of the current frame. By integrating the absolute value of this frame difference for every four regions of one picture plane, a table of frame difference integration data of each region is obtained. The location of the minimum value in this frame difference integration table is detected as a movement vector of that region.
Conventional apparatus for detecting a movement vector of a television camera have the following drawbacks as mentioned hereinafter.
First, reliabilities of the movement vectors derived from the frame difference integration table of each region differ in dependence on the picture in that region. For instance, in the region having a large amount of low frequency components, such as a sky or a sea, the distribution near the minimum value has a gradual slope in the frame difference integration table and a reliability of movement vector is low. On the contrary, in the region having a large amount of high frequency componets, such as a fine picture, the distribution is steep and a reliability of movement vector is high. Conventional apparatus do not consider such a difference in reliability due to the content of respective pictures.
Second, since the degree of influence of noise, moving objects or the like in respective regions will differ, the detection accuracies of movement vectors in respective regions will also differ. Practically speaking, in the region where there is little noise and few moving objects, the frame differences regarding almost all of the pixels become minimum at the position of the movement vectors, so that the distribution having a single extreme value is obtained. On the contrary, in the region where there are large noises and many moving objects, the distribution of the frame differences has a plurality of extreme values, so that the accuracy of the movement vectors detected in such a region is low. In conventional apparatus, such influences of noises, moving objects, etc. are not considered.